Heat corrosion resistant metallic material



PutentedNov. 3, 1942 HEAT CORROSION MATE Rea A. Axline, Forest Hills, N. Y., assignor'to Metailizing Engineeringv Company. Inc., Long Island City, N. Y., a corporation of New Jersey No Drawing. Application June 26, 1940, Serial No. 342,457

16 Claims. (01. 111-51) This invention relates to new and useful im provements in heat corrosion resistant metallic materials.

Many metallic materials are used in places where they are exposed to high temperatures and the influence of corrosive gases such as oxydiz- 1118 s s. particularly air and air or oxygen containing gases as well as the combustion products from coal, oils, gas or other fuels. These materials and especially those of a ferrous and cuprous nature, when exposed to such corrosive gases at relativelyfhigh temperatures, corrode very rapidly so that their useful life is, as a rule, relatively short. Ordinary carbon steel, for instance, will only last a few hours in a conventional gas furnace at temperatures between 1500 and 2000" F. before the surface of the steel becomes badly corroded and scaled. Furnace parts, grate bars, carburizing pots, furnace rail truck parts, hot salt baths and tanks, melting crucibles. casting molds, pyrometer protection tubes, engine exhaust manifolds and pipes. and pouring ladles, consisting of or containing copper, iron, steel or alloys thereof, are only a few examples of parts which are commonly exposed to corrosive gases, while at or exposed to relatively high temperatures.

The corrosion and scaling of articles consisting of or containing ferrous or cuprous materials as the result of the deleterious action of corrosive'gases, at relatively high temperatures, is commonly called heat corrosion. I have discovered that objects consisting of or containing ferrous or cuprous materials may be obtained that are substantially resistant against heat corrosion.

In accordance with the invention a heat corrodlble ferrous or cuprous object is first provided with a relatively thin coat of a nickel chromium alloy by metal spraying, whereupon the thusly coated object is provided with an aluminous coating, 1. e., a coating consisting of or containing metallic aluminum.

The process of metal spraying is well known in the art and comprises propelling metal particles in a molten 01' heat softened condition by means of a blast of air or other gas against the surface or object to be coated.

In carrying out the invention the object to be coated is preferably thoroughly cleaned and roughened before the sprayed metal is applied. The preferred method for cleaning and roughening the surface of the object is to blast it with a grit blast in accordance with well known prac- RESISTANT METALLIC BIAL roughened by other means such as by pickling, acid etching, machining, or the like. It is possible to eliminate the roughening of the surface, provided the surface is thoroughly cleaned, and to cause adhesion of the sprayed metal particles to the surface by heating the same to a sumciently high temperature. A suitable nickel chromium alloy is applied to the cleaned metallic surface by metal spraying until a coating of satisfactory thickness has been obtained. In many cases a thickness of .005 inch or less will ve satisfactory heat corrosion resistance. The coating is preferably at least .010 inch thick.

The upper limit of the thickness of the coatin is to some extent dependent upon factors involving the chipping of, and thermal stresses in the coating. In general a thickness not materially in excess of .025 inch is preferred for this reason.

Within the broad purview of my invention any chrome-nickel alloy may be used for spraying the first coating onto the ferrous or cuprous object. I prefer, however, to use an alloy containing substantially 10 to 20% chromium and 25 to 80% nickel. Suitable alloys are, for instance. alloys of the following approximate compositions; 67% Ni, 16% Cr, 16% Fe, 1% Mn; Ni, 12% Cr, 26% Fe, 2% Mn; Ni, 20% Cr; 25% Ni, 17% Cr, 2.5% silicon, 55.5% Fe; 80% Ni, 14% Cr, 6% Fe; 62% Ni, 15% Cr, .2% C, 2% Mn, .35% silicon, 20.45% Fe.

After the chromium nickel alloy has been applied by metal spraying, the coating of aluminous material is applied to the alloy coating. This coating of aluminous material may be applied in any one of a number of ways. For instance, it may be applied in the form of an aluminum paint, i. e., a dispersion of finely divided metallic aluminum in a vehicle or carrier such as oil, bituminous liquid or the like. When resorting to the aluminous material in the form of a paint I prefer to use a bituminous aluminum paint. Such paint may be applied to the surface with a brush or blown on with a paint spray gun or applied in any other suitable manner, such as by dipping. The applicationof the aluminous matter in the form of an aluminum paint is an effective yet inexpensive method of applying the aluminous coating.

Another and preferred method of applying the aluminous coating to the coating of chromium nickel alloy is to apply the aluminous material tices. The surface may, however, be cleaned and 55 by spraying metallic aluminum. As spray metal will adhere to a spray metal surface, no additional cleaning or roughening of the sprayed alloy surface is required and the aluminum may be sprayed directly onto the same. Where the aluminum is applied by metal spraying, an aluminum coating having a thickness of between .001 inch and .008 inch has been found satisfactory. "In many cases it has been found advantageous, particularly where the aluminous coating is applied by metal spraying to use aluminum ofhigh purity.

For most purposesa single coating of aluminous material, whether applied by metal spraying or in the form of an aluminum paint, or otherwise, has been found satisfactory. For best results, however, and still higher resistance against heat corrosion, I have found it advantageous to first apply to the chromium nickel alloy coated object a coating of metallic aluminum, preferably by spraying and thereafter applying onto this aluminous coating a coating of aluminum paint and preferably of bituminous aluminum paint by either brushing, spraying, or dipping.

Where in the specification and claims reference is made to a ferrous material, or to a cuprous material or where expressions of similar import are used, it is intended to designate thereby a material consisting of or containing metallic iron or metallic copper respectively, and irrespective of whether such material consists of or contains such metallic iron or metallic copper as substantially pure metal or in alloy form.

Where in the specification and claims the term "metallic aluminum material or such similar expression is used, the same is intended to connote any material consisting of or containing metallic aluminum, whether as substantially pure metal or in alloy form, and irrespective of whether'the aluminum is present in finely divided form dispersed throughout a carrier includinga bituminous carrier or whether the same is present in sprayed or other form.

It is sometimes of advantage and special circumstances may recommend to subject the objects coated in accordance with the invention to a heat treatment by heating the same to a temperature in excess of approximately 1200 F. and below the melting point of the f crrous or cuprous material and preferably to a temperature between 1600" F. to 1700 F., thereby still further enhancing the heat corrosion resistant properties of the treated object.

The objects treated in accordance with the invention are substantially resistantto corrosion at relatively high temperatures. It is not always necessary to coat the entire object and it suffices in many cases to treat those parts or surfaces that are to be exposed to heat corrosion. For large carburizing pots, for instance, it has been found satisfactory to coat the outside bottom of the pot only where it is exposed to the heat and gases from the furnace. The top edges of the pot are not exposed to high temperatures and the inside of these pots is protected from gases by their contents. Objects made of plain carbon steel have been coated in accordance with the invention and have successfully withstood heat corrosive action in a gas furnace at temperatures of 2000 F. and higher for over 300 hours, whereas similar plain uncoated carbon steel pieces exhibited bad scaling and heat corrosion under the same conditions in less than four hours.

The following specific examples of the practical application of my invention furnished by way of illustration and not of limitation demonstrate theheat corrosion resistance of a bar of steel approximately 1 inch in diameter by 4 inches long treated in accordance with the invention:

J Example I The bar was cleaned and roughened by grit blasting. It was then provided by the conventional metal spraying process with a coating of sprayed chromium-nickel alloy to a thickness of .010 inch. The chromium-nickel alloy was in wire form before spraying and had an analysis of 15% Cr, 62% Ni, 20.45%Fe, 2% Mn, 35% silicon and .2% C. Thereafter a coating of bituminous paint containing finely divided metallic aluminum was appied by brush to the outside of the sprayed chrome nickel alloy coating. The coated bar was then placed in a gas furnace at a temperature of approximately 2000 F. The

piece withstood the corrosive effect of the gases in the furnace for over 180 hours.

Example II A steel barof substantially the same size and material as that used in connection with Example I was coated with the same chromium nickel alloy in the manner there described. High purity aluminum was then applied by the conventional metal spraying process-onto the outside of the chrome nickel alloy coating to form an aluminum coating of approximately .006 inch thickness. The bar was then furnace treated as described in the preceding example at a temperature of 2000 F. No appreciable scaling occurred up to approximately 280 hours.

Example III A steel bar of substantially the same dimensions and material as used in the preceding examples was provided with substantially the same chromium nickel alloy spray coating and thereafter with a coating of sprayed aluminum, both coatings being applied in substantially the same manner and thickness as described in connection with Example II. Thereafter a coating of a bituminous paint containing metallic aluminum particles was applied by brush to the outside of the sprayed aluminum coating. The bar A piece of the same steel, both as to dimensions and compositions as was used in Examples I, II and III was placed uncoated in the same furnace at 2000 F. At the end of four hours bad scaling appeared to an appreciable extent.

'I'he'foregoing description is for purposes of illustration and not of limitation, and it is, therefore, my intention that the invention be limited only by the appended claims or their equivalent, wherein I have endeavored to claim broadly all inherent novelty.

I claim:

1. An article of manufacture comprising an object at least a portion of the surface of which comprises at least one heat corrodible metallic material of the group consisting of ferrous and cuprous materials, a relatively thin spray metal coating of a chromium nickel alloy on at least a part of said surface portion and superimposed on said alloy coating a coating of metallic aluminum.

2.'An article of manufacture in accordance with claim 1 in which said coating of metallic aluminum material is a coating of a bituminous paint containing finely divided metallic aluminum.

3. An article of manufacture in accordance with claim 1 in which said coating of metallic aluminum material is a spray metal coating of aluminum.

4. An article of manufacture comprising an object, at least a portion of the surface of which comprises at least one heat corrodible metallic material of the group consisting of ferrous and cuprous materials, a relatively thin spray metal coating of a chromium nickel alloy on at least a part of said surface portion, superimposed on said alloy coating a spray metal coating oflaluminum and superimposed on said spray metal coating of aluminum a coating of bituminous paint containing finely divided metallic aluminum.

5. An article of manufacture comprising an object, at least a portion of the surface of which comprises at least one heat corrodible metallic material of th groupconsisting of ferrous and cuprous materials a composite coating constituting the heat reaction product of a relatively thin spray metal coating of a chromium nickel alloy on at least a part of said surface portion, superimposed on said alloy coating a spray metal coating of aluminum and superimposedon said spray metal coating of aluminum a coating of bituminous paint containing finely divided metallic aluminum.

6. An article of manufacture 'comprising---an object of ferrous material, a spray metal coating of a chromium nickel alloy, substantially composed of from 10 to chromium and to 80% nickel, on at least a part of said-object and superimposed on said alloy coating a coating of me tallic aluminum material.

7. An article of manufacture-comprising an object of ferrous material, a spray metal coating of a chromium nickel alloy substantially composed of 10 to 20% chromium and 25 to 80% nickel, in a thickness of substantially .01" to .025 on at least a part of said object, superimposed on said alloy coating a spray metal coating of aluminum substantially .001" to .008" thickness and superimposed on said spray metal coating of aluminum a coating of a bituminous paint containing finely divided metallic aluminum.

8. An article of manufacture comprising an object of ferrous material a composite coating constituting the heat reaction product of a spray metal coating of a chromium nickel alloy substantially composed of 10 to 20% chromium and 25 to 80% nickel on at least a part of said object, superimposed on said alloy coating a spray metal coating of aluminum and'superimposed on said spray metal coating of aluminum a coating of a bituminous paint containing finely divided metallic aluminum.

9. Method for rendering surfaces, comprising atleast one heat corrodible metallic material of the group consisting of ferrous and cuprous materials, substantially resistant to heat corrosion which comprises applying to such surface a relatively thin coating of a chromium nickel alloy by metal spraying and thereafter applying to said sprayed alloy coating a coating of metallic aluminum material.

10. Method for rendering surfaces, comprising at least one heat corrodible metallic material of the group consisting of ferrous and cuprous materials, substantially resistant to heat corrosion which comprises applying to such surface a relatively thin coating of a chromium nickel alloy, substantially composed of 10 to 20% chromium and 25 to 80% nickel, by metal spraying and thereafter applying to said sprayed alloy coating a coating of metallic aluminum material.

11. Method in accordance with claim 10 in which said coating of metallic aluminum material is applied to said alloy coating by spraying aluminum thereon.

12. Method for rendering surfaces, comprising at least one heat corrodible metallic material of the group consisting of ferrous and cuprous materials, substantially resistant to heat corrosion which comprises applying to such surface a relatively thin coating of a chromium nickel alloy, substantially composed of 10 to 20% chromium and 25 to 80% nickel, by metal spraying, thereafter applying to said sprayed alloy coating a relatively thin coating of aluminum by metal spraying and finally applying to said sprayed aluminum coating a coating of a bituminous paint containing finely divided metallic aluminum. 7

13. Method in accordance with claim 12 in which all of said coatings after the application of said bituminous paint are heated to a temperature in excess of approximately 1200 F. and below the melting point of said metallic material.

14. Method for rendering surfaces, comprising a ferrous material, substantially resistant to heat corrosion which comprises applying to such surfaces a coating of a chromium nickel alloy, substantially composed of 10 to 20% chromium and 25 to 80% nickel, in a thickness of substantially .01 inch to .025 inch, by metal spraying, and thereafter applying to said sprayed alloy coating a coating of spray aluminum in a thickness of substantially .001" to .008".

15. Method for rendering surfaces, comprising a ferrous material, substantially resistant to heat corrosion which comprises applying to such surface a coating of chromium nickel alloy, substantially composed of 10 to 20% chromium and 25 to nickel, in a thickness of substantially .01 inch to .025 inch, by metal spraying, thereafter applying to said sprayed alloy coating a coating of aluminum substantially .001 inch to .008 inch thick, by metal spraying, and finally applying to said sprayed aluminum coating a coating of a bituminous paint containing finely divided metallic aluminum.

16. Method in accordance with claim 15 in which all of said coatings, after the application of said bituminous paint, are heated to a temperature of in excess of approximately 1200 F. and below the melting point of said ferrous material.

REA A. AXLINE. 

